Messier 72

Discovered by Pierre Méchain on August 29-30, 1780.

Messier: M72.

October 4, 1780. 72. 20h 41m 23s (310d 20' 49") -13d 20' 51"
Méchain: (310d 21' 10") -13d 21' 24"
`Nebula seen by M. Méchain in the night of August 29-30, 1780, above the neck of Capricorn. M. Messier looked for it on the 4th and 5th October following: the light is as faint as for the preceding [M71]; near it is a small telescopic star: the position was determined from the star Nu Aquarii, of fifth magnitude.' (diam 2')

William Herschel

[PT 1814 p. 274, SP2 p. 534]
October 30, 1810. 40 feet telescope. Space penetrating power 191.68. Magnifying power 280. "Having been about 20 minutes at the telescope to prepare the eye properly for seeing minute objects, the 72d of the Connoiss. [M 72 = NGC 6981] came into the field. It is a very bright object."
"It is a cluster of stars of a round figure, but the very faint stars on the outside of globular clusters are generally a little dispersed so as to deviate from a perfectly circular form. The telescopes which have the greatest light shew this best."
"It is very gradually extremely condensed in the centre, bit with much attention, even there, the stars may be distinguished."
"There are many stars in the filed of view with it, but they are of several magnitudes totally different from the excessively small ones which compose the cluster."
"It is not possible to form an idea of the number of stars that may be in such a cluster; but I think we cannot estimate them by hundreds."
"The diameter of the cluster is about 1/5 of the field, which gives 1'53".6." See fig. 17.

[PT 1818 p. 447-448, SP2 p. 600]
The 72nd of the Connoissance. [M 72 = NGC 6981]
"1805, 7 feet telescope. With a power of 80 the stars may just be perceived."
"1783, 1810, 10 feet telescope. With 150 fairly resolved."
"1784, 1788, 20 feet telescope. A cluster of very small stars."
"1810, large 10 feet telescope. A globular cluster; its diameter is 2' 40"."
"1810, Oct. 30, 40 feet telescope. A beautiful cluster of stars." [For further particulars see above, 1814]
By the observation with the 7 feet telescope, the profundity of this cluster must be of the 243d order.

[Unpublished Observations of Messier's Nebulae and Clusters. Scientific Papers, Vol. 2, p. 659]
1810, Oct 30, Review. 40 feet. Having been about 20 minutes at the telescope to prepare the eye properly for seeing critical objects, the 72nd of the Connois. came into the field. It is a very bright object. It is a cluster of stars of a round figure, but the very faint stars on the outside of these sorts of clusters are generally a little dispersed so as to deviate from a very perfect circular form; the telescopes which have the greatest light shew this best. It is very gradually extremely condensed in the center, but with much attention even there the stars may be distinguished. Power 280. There are many stars in the field of view with it, butthey are of many magnitudes and totally different from the excessively small [faint] ones which compose the cluster. It is not possible to form an idea of the number of stars that may be in such a cluster, but I think we cannot estimate them by hundreds. The diameter is about 1/5 of the field = 1' 53.6". - 10 feet telescope. I viewed the same object. The contrast is very striking, it appear eF [extremely faint].

John Herschel (1833): h 2090.

h 2090 = M72.
Sweep 10 (October 4, 1825)
RA 20h 44m 5.1s, NPD 103d 10' 26s (1830.0) [Right Ascension and North Polar Distance]
F; R; gbM; resolved into very small stars; 2 or 3' diam.
Faint; round; gradually brighter toward the middle; resolved into very small [faint] stars; 2 or 3' diameter.

Sweep 363 (August 6, 1831)
RA 20h 44m 5.8s, NPD 103d 10' 9s (1830.0)
pB; v compressed cluster; irreg R; barely resolved; vgbM; 3' diam; many straggling stars near, but none so small as those of the cluster.
Pretty bright; very compressed cluster; irregularly round; barely resolved; very gradually brighter toward the middle; resolved into very small [faint] stars; many straggling stars near, but none so small as those of the cluster.

Sweep 34 (July 31, 1826)
RA 20h 44m 6.5s, NPD 103d 10' 13s (1830.0)
F; R; 2' diam; gbM; r, but I do not see the stars separated enough to count them. Sky beautiful. Has a * 9m 30 deg sf, dist 3'. Is rather an insignificant object.
Faint; round; 2' diameter; gradually brighter toward the middle; resolvable [mottled, not resolved], but I do not see the stars separated enough to count them. Sky beautiful. Has a star of 9th magnitude 30 degrees sf, distance 3'. Is rather an insignificant object.

Smyth: DCCLXVI [764]. M72.

DCCLXVI. 72 M. Capricorni [now Aquarii].
AR 20h 44m 39s, Dec S 13d 07'.6
Mean Epoch of Observation: 1836.72 [Sep 1836]
A globular cluster of minute stars between Aquarius and the neck of Capricorn; being 9 deg due east of Alpha Capricorni, where it follows, at about half a degree, 325 P. XX, a star of the 6 1/2 magnitude [from Piazzi's catalog]. There are many telescopic stars in the field, a small pair of which closely follows the cluster. This object was discovered by the astronomical ferret M. Messier in 1780, and registered as a nebula: three years afterwards WH resolved it into stars, with his 20-foot [FL] reflector; and on gauging, he pronounced its profundity to be of the 243rd order. It will show the reader the care and attention of Sir William, to give his next observation of this cluster, with the giant-reflector:

October 4, 1810. 40-feet telescope. Space-penetrating power 191.68. Magnifying power 280. Having been a sufficient time at the telescope to prepare the eye properly for seeing minute objects, the 72d of the Connoissance des Temps [Messier's Catalog] came into the field. It is a very bright object.
It is a cluster of stars of a round figure, but the very faint stars on the outside of globular clusters are generally little dispersed, so as to deviate from a perfectly circular form. The telescopes which have the greatest light show this best. It is very gradually extremely condensated in the centre, but with much attention, even there, the stars may be distinguished.
There are many stars in the field of view with it, but they are of several magnitudes, totally different from the excessively small [faint] ones which compose the cluster. It is not possible to form an idea of the number of stars that may be in such a cluster: but I think we cannot estimate them by hundreds. The diameter of the cluster is about one-fifth of the field, which gives 1' 53".6.

This cluster is followed, at about 5m difference AR and 7' to the southward, by a trio of 10th-magnitude stars in a poor field: this is No. 73 of Messier's list, also registered in 1780.

John Herschel, General Catalogue: GC 4608.

GC 4608 = h 2090 = M 72.
RA 20h 45m 44.9s, NPD 103d 3' 35.8" (1860.0) [Right Ascension and North Polar Distance]
Glob. Cl.; pB; pL; R; gmCM; rrr. 10 observations by W. & J. Herschel.
Globular cluster; pretty bright; pretty large; round; gradually much compressed toward the middle, well resolved.

Dreyer: NGC 6981.

NGC 6981 = GC 4608 = h 2090; Méchain, M 72.
RA 20h 45m 44.9s, NPD 103d 3' 35.8" (1860.0) [Right Ascension and North Polar Distance]
Glob. Cl., pB, pL, R, gmCM, rrr; = M72
Globular cluster, pretty bright, pretty large, round, gradually much compressed toward the middle, well resolved.

Curtis

[Descriptions of 762 Nebulae ans Clusters photographed with the Crossley Reflector. Publ. Lick Obs., No. 13, Part I, p. 9-42]
NGC 6981, RA=20:48.0, Dec=-12:55. Small bright cluster 3' in diameter; globular; comparatively open. 13 s.n.